GS 850 Woes

[veedub]

Bear with me I think this is going to be a long one.

I bought a '79 gs 850 a couple weeks ago that I have been trying to get running. Supposedly it was a runner two years ago and last summer it was started a few times but never ridden. When I got it it would not start except for on starting fluid.

There seemed to be weak or intermittent spark problems going on so I replaced the points and condensers. Spark seems strong blue/white now.

Problem One, If I set (statically) the timing on 1/3 I cant quite get 2/4 to be spot on I will be about 1mm advanced on 2/4. I can split the difference and have them both off a bit but I cant get them both spot on. I cant get it running long enough to get a strobe check.

I rebuilt the carbs. 2,3,and 4 were dirty but ive seen worse on running vehicles. #1 was filled with clear goo (congealed gas? or?)They are all spotless clean now inside and out. They are VM carbs as its a '79. The only thing I did not takeout and clean where the chokes as I had never seen a choke like that and didn't know how to disassemble it and my manual was no help. I later found a great tutorial on this site but the carbs were already back together at that point they all move freely and when I do get it running for short bursts changing the choke setting does effect running so I know they are working.

The settings for the fuel and air needles were all over the place from 1.25 to 2.25 turns out for the fuel pilot screws the air pilots were closer to equal with settings from 1.25 to 1.75. From what I have read 1/4 turn on the fuel needles is a big difference so it seems strange they would be up to a full turn different. I did not keep track of which needle came out of which carb not sure if this matters. They did not have paint on them so they very well could have rattled themselves to a new setting over the course of the last 30 years. Anyway I have tried setting them from the settings they originally had and combinations of what was in this tutorial from one end of what he says are normal settings to the other.

http://www.thegsresources.com/files/vm_carb_rebuild.pdf

At one point I had it running if I just barely cracked open the throttle (idle was possibly set a hair low at this point) but if I opened the throttle at all it would begin to choke out. However It was running on 2 cylinders only. What really struck me as odd was that the cylinders it was running on were 3&4 if it was an ignition related problem I would think it would run on 1/3 or 2/4 so this problem must be carb related? At the time it was running like this all carb screws were set at equal settings I think 1.5 turns out on the fuel screws and 1.25 on the air screws but I am not positive on those numbers.

I don't have any true compression numbers since I can never get it to run long enough to get up to operating temp but a stone cold compression test showed around 120lbs on all cylinders.

The valves are all a bit tight or atleast I think they are. the smallest feeler gauge I own is .002 inches and according to my manual low limit is .0012 I cant get the .002 in there but the shim will spin freely so I dont think its under any tension there must be atleast around .001 of an inch of clearance for this to be true right? I also have a question on checking valves the manual says turn the cam lobe perpendicular to the head and shows a picture however this is different than perpendicular to the shim which is set at an angle and thus if u set the cam lobe perpendicular to the shim u come up with a bit more clearence. What is the correct check? I don't have a tappet depressor tool or any replacement shims(yet) so Id be SOL to fix them right now even if they are a hair tight)

So to sum up:

1. Cant get timing right on both sets
2. Can only get running on 3/4 This has to be a carb problem right?
3. Proper cam lobe position to check valves.
4. Any other ideas, tips, shots in the dark to try to get it running.

[kdo58]

everything you wanted to know and more

http://members.dslextreme.com/users/bikecliff/

[azr]

Great bike you've got there.
Points; first off it's cylinders 1&4 fire together and the 2&3. Not as you had it in your post. 1&4 is the points on the left when you're looking at your igntion, the right one is for 2&3. I've had similar problems with 2&3 before, almost spot on but not exactly, the problem was I didn't have my points gapped properly. Once I redid them 2&3 lined up better, but they were maxed out to the extent of being adjusted to their extreme.
Carbs;your're chokes might be ok but you really never know until you unscrew them, they're easy to get out when the carbs are apart. The fuel needles are fine to swap around as long as they are in good shape. Make sure none of their tips are broken (hopefully not stuck in the carb). Did you check all your float needles as well? making sure they are not flattened out. Did you adjust your floats? and if so did you measure them dry or use the clear hose method with fuel in the carbs? Float height can effect performance and starting of course. Your fuel mixture and air mixture screw are still adjusted wrong. Fuel should be around 5/8 and air about double at 1 1/4. That gets you started and you fine adjust from there once the bike is up and running. When you say they are spotlessly clean, does that mean you dipped them? if so your chokes may need some attention as the rubber doesn't like carb dip and if you didn't dip them then there is a good chance some of the inlets are still pluged. How do your plugs look? are they getting fuel? Spark fuel and air is all she needs to run.
valves; the acceptable variations for your valves are 0.03 - 0.08 mm. anything in there is acceptalbe, some people even go a bit more than 0.08. There is a step by step, clear as a bell, tutorial on Cliffs website on how to do valve adjustments, and how to use a zip tie to keep the valves open.
You should check your voltage getting to your coils. Anything less than 11 Volts and it maybe a bit too weak to have the bike running properly and you should think about doing the "coil mod". It's on Cliff's site as well. Have you looked at your airbox. If the original seals are not intact and the airfilter is clogged that will definately effect starting/running. On cliff's site again or under the search feature on here "air box rebuild"

Great to hear you're trying to put another one on the road. Read over Cliff's site and I'm pretty sure you'll get alot of answers. The search feature on here is great too. Let us know how things come or if you need some more help.

[veedub]

Sorry your right, 1,4 and 2,3 regardless 3,4 the ones I am firing on are not a matched pair. I will try to regap the points I gapped them to small tolerance .3mm but I will regap to them closer to the other end of the spectrum .4mm and see if that gets it closer. Looks like I'll pull the carbs back apart and check out the chokes. I did dip them but not conventionally I boiled them for 20 mins in a 50/50 solution of lemon juice and water. The acidity cleans and removes everything and its not harsh enough to mess with your rubber parts. I will retry with the settings you suggested
I know the valve tolerences are .03-.08 which is .0012-.0030 on the standard system. Unfortunately on my three feeler gauge sets I don't own anything lower than .002 (standard) I will check out that tutorial

Ill check coil voltage

The airbox seals are terrible however I actually had the airbox removed while I was doing this I have had plenty of engines running with no aircleaner on before they may run a bit lean but not enough to keep it from running at all. Do these slide carbs need to airbox installed to create the negative pressure needed to run that could be my problem right there if it makes that huge of a difference....

Also just to double check fuel screws are on the bottom and air are coming in diagonally from the top down torwards the bowl correct?

[azr]

Yup, fuel on the bottom and air on the sides. You're right, without the airbox you 'should' be able to start the bike (but sounds like an airbox rebuild is in order), the same as with the points, as long as they are 'close' you 'should' be able to at least start the bike. If it's only running on 3&4 then it is pointing to a carb issue. I've never boiled but I know lots of people on here have I'm just not sure of the time spent boiling, just makes sure you shoot all the inlets with carb cleaner to make sure they're cleaned out and have a good look at those fuel screw tips, they are known for breaking off in the carb body. You mentioned getting a good blue spark now, is that true for 1&2? as for the valves, they probably need adjustment but it sounds like shouldn't be stopping the bike from starting. It's probably all in the carbs. As long as you don't have any of the wiring or plug wires put on wrong? Just thinking out loud, how many times have I scratched my head over something to only find out it was the simplest thing. Good luck.

[veedub]

Ya maybe its a combination of all the shoulds lining up just right. An airbox rebuild is in order I would just really like to hear it purr before I dump any more money into it, but I'm sure it will get going so I guess yet another parts order needs to happen. I am with you I think if its only one and two not running all the other stuff needs to be fixed and addressed however its got to be in the carbs. All the fuel screw tips were still sharp and nice. As for boiling try it out, I have rebuilt quite a few carbs (vws and small engine this was a first for motorcycle) and this was the first time I tried the boiling trick but I am sold on it I will do it from now on. However I will be doing it outside on a campstove from now on, my house smelled like a gas station for two days...

[veedub]

Also thinking out loud, I did a preliminary cold compression check and got somewhere in the 120 ballpark for all cylinders its been my experience a cold compression check is virtually useless for true numbers but I didnt come up with anything shockingly low either. However in cliffs tutorial on valve changing it says take out all spark plugs or else you wont be able to turn the engine over by hand with the 19mm wrench. I have turned the engine over plenty with the wrench while setting points and checking valves and I mean its not easy to the point of spinning it round and round with one hand but its certainly not overly difficult either. Also this is the first bike I ever owned with a kick start I expected it to be a bit harder to kick over than it is. Hoping I don't have a compression issue to deal with. But once again even if compression was a bit low the bike "should" still start and run even if performance was compromised. Everything still tells me this must be a carb issue. Now Ive got to get a new valve cover gasket so I can put that back on and try to start it with new carb settings.

[azr]

Your cold compression test is the same on mine, 120, hot is a bit higher. To kick start these bikes it is surprisingly easy so don't worry about the compression. I remember sitting beside an old 62 Harley and he was attempting to kick start the thing, holy cow, I thought he was going to have a heart attack. I thought for fun I would kick mine as well..ha,ha,ha,ha. I swear it's harder to kick over my KH100 than it is my 850. The same with turning it over with the plugs in, it's a lot easier with them out of course but you don't need to. The next rack of carbs I have to do I'll have to try the boiling method, it's cheaper than carb dip that's for sure. Let us know how things turn out.

[BassCliff]

Hi,

I must admit that I don't take the plugs out any more when adjusting the valves. It's not that hard to turn the engine.

Thank you for your indulgence,

BassCliff

[cowboyup3371]

Hi,

I must admit that I don't take the plugs out any more when adjusting the valves. It's not that hard to turn the engine.

Thank you for your indulgence,

BassCliff

Thanks Bass...I thought I was the only one who left them in. Glad I didn't make a serious mistake then.